Process for the manufacture of sulphuric acid



Oct. 14, 1941. H. PETERsEN 2,258,938`

PROCESS FOR THE MANUFACTRE OF SULPHURIC ACID Filed June 2, .1958

By// l u Attorney.

atenteci i4,

UNITED STATES PATENT Pnocnss Fon THE MANUFACTURE oF SULPHURIC Aon) Hugo Petersen, Berln-Steglitz, Germany Application June 2, 1938, Serial No. 211,439 In Germany September 27,1937

1 Claim.

This invention relates to a process of and apparatus for the manufacture of sulphuric acid.

In recent times attempts have been made to increase more and more the load in chamber systems per cubic metre of hollow space and also the load in tower systems per cubic metre of iilling space, by suitable measures. Thus, when manufacturing in chamber systems, the load has been brought up to 15 kgs. of sulphuric acid of '78% strength per cubic metre of chamber space in 24 hours, and in tower systems to 60 kgs. per cubic metre of useful tower space. In combined chamber and tower systems the output of the chamber space was further increased.

The present invention enables these loads t be further considerably increased. The invention aims at replacing, in chamber systems, principally the last chambers, in which the reaction is very sluggish, by towers, in such a way that, proceeding in a forward direction, increasingly more chambers are cut out. In addition, the number of the Glover and Gay-Lussac towers is to be increasingly restricted, principally by the use of suitable filling material, until finally only one Glover tower and one Gay-Lussac tower remain.

Further details of the invention will become apparent as the description thereof proceeds. In order more clearly to understand the invention, reference is made tothe accompanying drawing, which illustrates diagrammatically and by way of example, several embodiments thereof.

In Figs, 1 to 3 those parts of the system which are to be omitted in accordance with the intensication to be increased are shown in broken lines. The gas path passing through all chambers is indicated by a full line furnished with arrows, while the two acid paths, going only through the towers and separated from each other, are indicated by chain dotted lines furnished with arrows.

Fig. 1 shows an apparatus for manufacturing sulphuric acid by means of nitric oxide (NO), comprising a plurality of Glover towers (of which the towers I and 2 are shown), a plurality of chambers 3, a tower 4 for the formation of the sulphuric acid, with lling space 4b and reoxidation chamberY 4a, a tower 5 for the combining of the nitrose, with reoxidation chamber 5b and filling chamber 5a, and a plurality of Gay-Lussac towers, of which the towers 6 and 'l are shown. The towers 4 and 5 form an inner production system, which is irrigated independentl'y in a circular flow and inserted in the gas path of an outer production system formed by the vremaining partsv and irrigated separately and likewise in a circular ow.

Fig. 2 shows the same appar-atus witha. modification consisting in that the oxidation chambers 4a and 5b are joined together to form a common chamber 8.y Said chamber 8 may be void or else filled. The inner, independently irrigated production system consists in this embodiment of the parts 4, 8 and 5.

Fig. 3 shows once more the same apparatus, but with the difference that the towers`4 and 5 are combined into a single tower 9, which contains the filling space VIl? for the formation of the sulphuric acid, the reoxidation space 8 (or 4a and 5b) and the filling chamber Safor combining the nitrose, and which-forms by itself the inner, independently irrigated production system. Y l

As already mentioned, the outer production system may be reduced, by optional omission of kthe parts shown in broken lines-for example the Glover tower l, the chambers 3 and the Gay- Lussac tower 'l-to a system having only two independently irrigated towers, namely the Glover tower 2 and the Gay-Lussac tower 6.

The irrigation of the outer production system is preferably effected with an acid of '78% strength, and that of the inner production system with an acid of about strength. The irrigation of the inner productiony system must be eiected in such a way that the acid of the production tower, on discharge, may not under any circumstances have the same oreven higher nitrose content as on supply. The difference should, on the contrary, be as large as possible, in order to liberate or keep liberated as much nitric oxide -as possiblein order to effect rapid regeneration. 'I'he acid running olf from the production tower 4 should containfrom 10 to 40% less nitric oxide than the acid running off in the following tower. The decrease may be as large as is consistent with lcomplete working up of the sulphurous acid. As, however, the cooling of the gases is also important to rapid regeneration, a filling layer will also be provided in the upper part of the production tower 4, in which layer the cold acid trickling down, in addition to working up any small traces of SO2 still present, substantially exerts'a cooling action. Ir-v rigation in counterow is essential in this case.

Between the production tower 4 and the tower 5 a suitable reoxidation space is to be provided, which needs to be the smaller, the stronger and colder the NO gas is. Thisreoxidation space can be disposed above or below or else aboveand below the tower 4 and the tower 5, but it may also be placed in a special chamber.

If a special chamber or tower (Fig. 2, tower E) is provided, it may be furnished with lling bodies and irrigation with nitrose acid be provided. but the latter may be only of such a strength that practically no N203 is withdrawn from the gas. The nitrose content should remain approximately at the same level when passing through the tower, so that on running off it is not higher than when running in. If this is complied with, the strength of the acid can be kept between 68 and 75%. to the knowledge that even an acid of only 60%, which hitherto was not considered as nitroseforming, forms a nitrose content-active even at this low concentration-of over. 0.2 %,referred Experiments have led to acid of 50%, given a high N203 contentfof the.

gases. The last residues of sulphur dioxide are particularly easily absorbed and worked up'by'ia cold acid of the concentration mentioned, the nitrose content beingcorlstantly reformed;

The inner production Systcmformed in this way sho'uld take lup at least 76% of the total production and,` ifV possible, 90% of, the regenerated oxides of nitrogen, while the outer production system efectsat most 30% ofthe production inthe Glover tower, and the Gay-Lussac tower should, as far as possible, not receive for absorption more than ofthe oxides of nitrogen leaving the inner ,main production tower. The effect of this is that the Glovertower, which receivesA its nitrose (apart from the nitrose production acid) from the last Gay-Lussac tower with a weak nitrose contentalso liberates only a' little NO gas, which ,can reoxidise only to a slight extent on the path to the main production tower. The further effect of this measure is that by far the greatest part of the production in the tower 4 is concentrated on to a small space having a large surface and a small hollow space unfavourable to reoxidation, with an extremely violent reaction likewise unfavourable to reoxidation, so that for this reason gases having a high NO content, favourable to reoxidation, issue from this tower. i

' The production yield in the Glover-tower up to is s till-arnllrly;high.` It is elected' by the denitration of the production acid` (produced with a nitrose content) ofthe inner main production tower 4. A reduction of this nitrose content can beI achieved` by depressing as far as possible the nitrose content in the inner production system. Inaddition, the production yield of th'e Glover tower may be still further diminished, by feeding theY acid from the last Gay-Lussac tower to the Glover tower in aj warmed up state, instead of a cooled state, whereby the gases leave the Glover tower at considerably higher temperatures. Y This artificial raising of,l the temperature may proceed up to 100. Both the production action andthe reoxidation of the oxides of nitrogen are thereby suppressed, both-of which effects promote a high NOV content on issue from theinner production tower 0l. The heating of `,the AGay-Lussac acid passing to the Glover tower may be 4eijected by the hot-'acid flowing out of the Glover tower, or also by meansYof-the acid of the'rst Gay-Lussac tower.

Apart from the aforedescribed arrangement of the apparatus and its irrigation, the correct choice of the filling bodies is of greatimportance to the rational performance of the sulphuric acid formation. Hitherto, when selecting the iilling bodies in the .production tower, the importance of 7:51

epesses the space left therebetween had been overlooked, and a relatively large hollow space had been left, in which the NO liberated during the formation of sulphuric acid had an opportunity of exten sively oxidising into N203 and of being reab sorbed in the irrigation acid. The requirement had even been imposed that the acid supplied to the tower should still possess the same nitrose content on passing out. The gases passing out of this tower consequently contained only small amounts of NO, which corresponded to the oxides of nitrogen escaping from the preceding Glover tower, but which oxidised only poorly on account of their low concentration. In order to obtain as high as possible an NO content from the sulphuric acid formation zone, in contradistinction to previous methods the oxidation of the NO and a recombining must be prevented to a great extent. This is achieved by keeping the proportion between the free space to the reaction surface, in the sulphurc acid formation zone, smaller than 5 litres per square metre, and this proportion may be reduced to such an extent that only l litre goes to l square metre, and this can be achieved by the selection of suitable llingbodies. As the oxidation of the SO2 and the absorption of the N203 represent an interfacial reaction between gas and liquid, the thus reduced passage for the gases is also Aof great importance. The smaller the gas passages are, the more easily contact between the gases and the irrigated surfaces occurs, the more rapidly the SO2 gases will dissolve in the liquid `and the more rapidly the formation of sulphuric acid will be completed. The surface of the filling bodies is considerably enlarged, by comparison with previous arrangements, in which only filling bodies having a surface ofy up to square metres per cubic metre of filling were known; when using particularly well shaped filling bodies with little empty space, the useful surface is increased to 600 square metres per cubic metre of filling space. In consequence, the reaction space may be considerably reduced.

The towers or spaces used for the combining of nitrose may also advantageously have the same lling as the sulphuric acid formation zone.

The tower 8 in Fig. 2 may be so designed that it is given filling bodies over the whole filling height available, said bodies leaving at least 60% free spacefor the reoxidation. However, it may be only half filled with a filling leaving a smaller hollow spacethan 60%, while the remaining half remainsfree for the reoxidation of the oxides of nitrogen.

In the embodiment shown in Fig. 3, the spaces la and 5a of the tower 9 are provided with filling bodies having as large a surface as possible and small gaps, as required above, for example with fine cruinbly material, and the space 8 (4b and 5b), on the other hand, is provided with filling bodies having a smaller surface but gaps as large as possible (for example irregularly poured` rings). The lling bodies of the lastmentioned space are preferably given only a fraction of the irrigation surfaces of the spaces 4a and 5a. The irrigation acid must in this case principally be directed to the requirements of the spaces a and 5a. The filling material holds up the movement of the acid in the zones 5a and 4a in a manner advantageous to the formation of acid, and this can be further promoted by counter-pressure to the gas movement, while the gases in the zones lb and 5b encounter only slight resistance or none at allI and thus areable to remain longer in the hollow spaces between the i'illing bodies, which is favourable to reoxidation. The resistance constituted by the filling bodies in the zones 4c and 5u and the consequently retarded ow of the acid enable substantially less acid to be pumped up to these Zones than heretofore and thus to save energy in raising the acid.

As a certain hollow space is still present in the sulphuric acid formation zone, the reoxidation of a small proportion cannot be entirely avoided, but this always amounts to only a fraction of the amount otherwise obtained. This small proportion can be further lessened by reducing the oxygen of the roasting gases. For example, when otherwise it is possible to reckon with '7% gases, the gases will be raised to 10% of sulphur dioxide producing a correspondingly lower oxygen content. The further advantage is then obtained that the total amount of the gas is quite considerably reduced, which again results in quite a considerable increase of the reaction. The same proportion may be taken for this increase as the increase of the SO2.

In each of the drawings the gas paths are shown in full lines as indicated at I while the acid paths are indicated by broken lines as shown at Il, I2, I3, I4, I5 and I6. Thc line I5 connects the inner production zone to the line II and thus to the Glover tower 2. This diverts a portion of the acid from the inner Zone and conducts it to the outer acid. The line I6 aiords draw-off means for a portion of the product from the Glover tower.

In the operation of a sulphuric acid plant irregularities often occur in consequence of inadequate roasting work, these irregularities aiecting both the amount of gas and the proportion of oxides of nitrogen contained therein. If these irregularities occur even in the normal roasting of pyrites or other sulphurised ores, they increase quite considerably in the case of metallurgical exhaust gases. In this case it is naturally impossible always to obtain in the reoxidation chamber a cooled gas high in nitric oxide. The reoxidation chamber provided in accordance with Figs. 2 or 3 between the towers of the inner production system, and furnished with lling bodies, has then a subsidiary function as regulator in order to perform the following functions:

1. Rapid solution and working up of the SO2 in acid of low concentration and having a sufficiently active nitrose content.

2. Su'icient hollow space for the reoxidaton of the oxides of nitrogen.

`3. Cooling of the gases, taking into account the heat of formation of the sulphuric acid.

4. Prevention of absorption of reoxidised nitric oxide.

The great technical and economic advantage of the various measures consists in the increasing of the output of a sulphuric acid system by a multiple per unit of space, as compared with previously known systems.

I claim:

A process for the production of sulphuric acid comprising passing SO2 gas in admixture with a relatively small quantity of nitric and nitrous oxides successively through a Glover tower, an acid production Zone wherein the greater proportion of the gases is dissolved and converted to sulphuric acid in a high nitrose containing acid, then in admixture with the reduced oxides of nitrogen set free by the converting acid to a reoxidation zone wherein the reduced oxides are oxidized, then through a combining or nitrose forming Zone wherein the oxides are removed, and finally through a Gay-Lussac tower, circulating one portion of acid successively through' the nitrose forming zone to remove the aforementioned oxides from the gas to form the aforementioned high nitrose containing acid, then through the acid producing Zone, and back to the nitrose forming zone, circulating another portion of acid in a cycle including the Gay-Lussac and Glover towers, heating the acid entering the Glover tower in order to expel nitrous oxide therefrom to enrich the gas leaving the Glover tower and oxidized in the reoxidation zone, maintaining the rst portion of acid at a concentration capable of dissolving SO2 gas and also of forming nitrose, and diverting a part of the first acid portion leaving the production Zone and low in nitrose into the second acid portion,

'i and wherein an oxidation zone is provided having at least of free space and independently sprayed with a cold acid of such strength that no N203 is withdrawn from the gas passing therethrough.

HUGO PEI'ERSEN. 

